Improvements in glass manufacture

Returned once more to dear old Baxter House, I came face to face with the débris of former mechanical investigations piled up here and there in some of the outbuildings, where quantities of old glass pots, and the ruins of a pair of large furnaces, lay scattered among heaps of wheels and pulleys on long shafts, and fragments of old iron framing. Each single piece of this wild mass brought back to memory the particular part it had played in one of those fierce contests with the mechanical powers, in which it may have come off victoriously, or, through want of foresight of the guiding mind, have been ignominiously beaten, to remain a mute witness to the shortcomings of so many plausible theories. Few men have made more mistakes than I have; perhaps there are few men who have so boldly grappled with absolutely novel problems about which no published data existed to guide and modify the first ideas whence all elaborate mechanical structures naturally spring, just as a plant does from its seed. There were many remains in this old storehouse which reminded me of investigations, interesting enough in themselves, but which I must leave wholly unmentioned if I am ever to arrive in this imperfect history at that part of my life's most energetic labours in which my colleagues of the Iron and Steel Institute are more immediately interested. So I must hasten on, and, in mercy to them, leave unsaid so much that I should have to tell if the limits of my little history, and the kind patience of my readers, permitted me to inflict it on them. The ventilation of mines by my combined steam fan, the centrifugal pumps which formed so interesting an exhibit in the International Exhibition of 1851; the compression of pure bituminous coal rendered plastic by superheated steam, and pressed into rectangular polished blocks by a continuous feeding and continuous discharge from a machine similar to the cane press: these and several other minor inventions must be passed over.

But there is one subject of deep interest that I desire to save from absolute oblivion, since its record may at some future time set some active and ingenious mind to work on the lines briefly indicated, and thus add another triumph to the many lately achieved in the domain of optical science.

For some years previous to the period of which I am writing, I was deeply interested in the question of "burning glasses," such as those of Buffon, Parker, and others; my aim being to construct an instrument of sufficient power to act on several ounces, instead of several grains, of the material, which was to be operated upon in crucibles, into which the focus of the lens was directed. In following up this idea, my attention was naturally turned to the enormous difficulty of producing perfectly homogeneous discs of optical glass of large diameters. Fraunhöfer's magnificent lenses of small size had for many years attracted universal admiration, and learned societies were intent on further investigation of the subject. Thus it was that Faraday commenced an enquiry which only ended in failure.

Fraunhöfer's system of manufacture was at that time a profound secret, and the small discs of glass which he sold at fabulous prices were the envy of all other optical glass makers. Faraday, whose scientific knowledge and attainments pointed him out as the most likely scientist to succeed in this new field of enquiry, was, I doubt not, led absolutely astray by the appearance of Fraunhöfer's small discs; had Faraday never seen one of them, and been left to his own resources, he would most probably have succeeded.

The small discs produced by Fraunhöfer, four or five inches in diameter and from half to three-quarters of an inch in thickness, showed what really appeared to be incontrovertible evidence that they were made in small open flat dishes, of the form shown in Fig. 21, page 102.

These little cakes of glass, a, had a flat shining upper surface, evidently the natural, or fire, polish, as it is called, and were rounded at the top edges as shown at b, the periphery of the flat cake and its lower surface having the unmistakeable impress of the shallow fireclay dish shown in section at c. These apparently irresistible proofs that the glass was made in small quantities, and was very fusible and very fluid, no doubt deceived Faraday, and so misdirected his experiments as to lead to failure; all of which became self-evident when the mode of producing these little cakes was known. Glass made in large pots and